Source : Webster's Revised Unabridged Dictionary (1913)

Water tube \Wa"ter tube`\ (Zo["o]l.)
   One of a system of tubular excretory organs having external
   openings, found in many invertebrates. They are believed to
   be analogous in function to the kidneys of vertebrates. See
   Illust. under {Trematodea}, and {Sporocyst}.

Water tube \Water tube\
   Any tube for passing or holding water; specif., in some steam
   boilers, a tube in which water circulates and steam is
   generated.

Tube \Tube\, n. [L. tubus; akin to tuba a trumpet: cf F. tube.]
   1. A hollow cylinder, of any material, used for the
      conveyance of fluids, and for various other purposes; a
      pipe.

   2. A telescope. ``Glazed optic tube.'' --Milton.

   3. A vessel in animal bodies or plants, which conveys a fluid
      or other substance.

   4. (Bot.) The narrow, hollow part of a gamopetalous corolla.

   5. (Gun.) A priming tube, or friction primer. See under
      {Priming}, and {Friction}.

   6. (Steam Boilers) A small pipe forming part of the boiler,
      containing water and surrounded by flame or hot gases, or
      else surrounded by water and forming a flue for the gases
      to pass through.

   7. (Zo["o]l.)
      (a) A more or less cylindrical, and often spiral, case
          secreted or constructed by many annelids, crustaceans,
          insects, and other animals, for protection or
          concealment. See Illust. of {Tubeworm}.
      (b) One of the siphons of a bivalve mollusk.

   {Capillary tube}, a tube of very fine bore. See {Capillary}.
      

   {Fire tube} (Steam Boilers), a tube which forms a flue.

   {Tube coral}. (Zo["o]l.) Same as {Tubipore}.

   {Tube foot} (Zo["o]l.), one of the ambulacral suckers of an
      echinoderm.

   {Tube plate}, or {Tube sheet} (Steam Boilers), a flue plate.
      See under {Flue}.

   {Tube pouch} (Mil.), a pouch containing priming tubes.

   {Tube spinner} (Zo["o]l.), any one of various species of
      spiders that construct tubelike webs. They belong to
      {Tegenaria}, {Agelena}, and allied genera.

   {Water tube} (Steam Boilers), a tube containing water and
      surrounded by flame or hot gases.